The intersecting chords theorem states that whenever two chords intersect, the product of their pieces is constant.
So, in this case, we have
Plugging your values, we have
This equation has solutions 
, but we can't choose 
, because it would lead to
So, the only feasible solutions is 
The answer is 80! If you ever see any angle like that where it’s just two lines (I don’t know how to explain it/forgot what it’s called) it will be the same as the other angle.
Radius is half the circumference
c= 2(square root) pieA
